Fuel cell stacks are used as an electrical power source in many applications. In particular, fuel cell stacks are proposed for use in automobiles to replace internal combustion engines. In typical applications, fuel cell stacks are provided in arrays of many individual fuel cells in order to provide high levels of electrical power. As the fuel cell stack is used, an undesirable drop in the stack output voltage is observed. It has been found that this voltage drop can be reversed by operating the fuel cell stack under wet conditions at a low voltage (i.e., at or below 30 V).
Several strategies have been devised for operating a fuel cell stack under low voltage conditions. In one prior art method, low voltage is achieved by running the fuel cell cathode at a low stoichiometry with accurate control of cathode valve positions to prevent the voltage from crashing. Another prior art method uses both a voltage suppression algorithm to bring down the voltage and a voltage limitation algorithm to keep the voltage from crashing. However, both strategies are proven to be ineffective to reach an aggressive cell voltage recovery target of below 300 mV per cell due to the hardware limitation, cell-to-cell variation, CAN signal transmission latency, and the like.
Accordingly, there is a need for fuel cell recovery systems that can maintain a fuel cell stack at a voltage that is useful for performing an effective voltage recovery.